Main article: X-linked recessive inheritance. She passed the harmful allele for this X-linked trait on to one of her four sons and at least two of her five daughters. Many of the non-sex determining X-linked genes are responsible for abnormal conditions such as hemophiliaDuchenne muscular dystrophyfragile-X syndromesome high blood pressure, congenital night blindness, G6PD deficiency, and the most common human genetic disorder, red-green color blindness.
All males possessing an X-linked recessive mutation will be affected, since males have only a single X chromosome and therefore have only one copy of X-linked genes. The "a" r ecessive allele will be expressed in his phenotype.
Namespaces Article Talk. Queen Victoria with her husband and nine children in By comparison to the X chromosome, the much smaller Y chromosome has only about 26 genes and gene families. All rights reserved. Most of the Y chromosome genes are involved with essential cell house-keeping activities 16 genes and sperm production 9 gene families.
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When any of the 9 genes involved in sperm production are missing or defective the result is usually very low sperm counts and subsequent infertility. This prevents mutant Y chromosome genes from being eliminated from male genetic lines except by inactivation or deletion.
Only females are able to be carriers for X-linked conditions; males will always be affected by any X-linked condition, since they have no second X chromosome with a healthy copy of the gene.